Two-dimensional variable area nozzles for vectoring the exhaust gases of a gas turbine engine are known in the art. Such nozzles are typically used in aircraft applications in which it is desired to achieve vertical or short takeoff and landing (V/STOL) operation. One such nozzle is shown in U.S. Pat. No. 4,392,615, "Viol (sic) Exhaust Nozzle with Veer Flap Extension" issued July 12, 1983 to Madden. Madden shows an exhaust nozzle having a rotatable hood type deflector for redirecting the engine exhaust gases downward. A movable ventral flap defines the variable nozzle throat between itself and the deflector hood during vectored thrust operation.
U.S. Pat. No. 4,375,276, "Variable Geometry Exhaust Nozzle" issued Mar. 1, 1983 to Konarski shows a vectorable nozzle having a pair of vertically opposed, articulated flap assemblies which are manipulated to vary both nozzle throat area and exhaust thrust direction. U.S. Pat. No. 4,052,007, "Flap-Type Two-Dimensional Nozzle" issued Oct. 4, 1977 to Willard shows a two-dimensional nozzle having a pair of vertically opposed flaps movable collectively between a position of maximum throat area and minimum throat area and a vertically opposed, centrally pivotable pair of downstream flaps movable both collectively and individually for directing the exhaust gases to achieve forward, reverse, modulated, or vectored thrust as desired.
The complexity of these prior art systems is immediately apparent, resulting from the large number of functional demands placed upon such nozzle arrangements. The vectoring of the thrust of a typically horizontally disposed gas turbine engine requires a duct or other structure which is physically strong in order to withstand the high gas pressures, thermally protected to withstand the high exhaust gas temperatures, and aerodynamically configured to provide the appropriate flow area and direction upon demand. Vectoring nozzles used in combination with augmented or other gas turbine engine arrangements requiring a variable nozzle throat area add an additional level of mechanical complexity by requiring the vectoring nozzle to also contract or enlarge the nozzle throat area at any thrust vector angle.
Thrust vectoring may be achieved either partially (up to 60.degree. from the horizontal) or fully (at least 90.degree. from the horizontal), depending upon the particular aircraft and desired operational characteristics. In either case, the vectoring of the exhaust gases downward is intended to support at least a portion of the aircraft mass by means of the vertical exhaust gas thrust component rather than through the use of the aircraft wing surfaces.
Typical engine arrangements place the engine exhaust nozzles aft of the aircraft center of gravity, resulting in a downward pitching moment during vectored thrust operation. One prior art design, shown in the Madden reference, actually moves the thrust vector aft during vectored thrust operation, exacerbating the downward pitching moment which must be counterbalanced to achieve stable aircraft operation.
An exhaust nozzle configuration which reduces this undesirable downward pitching moment during vectored thrust operation, which has a minimum number of moving flap surfaces in contact with the hot exhaust gas stream, and which, for augmented engine applications, is able to provide a selectable variable nozzle throat area throughout the entire range of vectored thrust operation is clearly a significant improvement over those nozzles defined in the prior art.